Civil and Building Engineering.

A soil is composed of mineral solids and voids. The voids may be filled water, other liquids, or gas (air). If all voids are filled with liquids, the soil is saturated.

If a stratum of clay exists above the water table, the position in the earth where water will collect in an open excavation, then the soil will be subject to wetting and drying, presenting a difficult problem to the engineer. If the clay is expansive, shrinking on drying and swelling on wetting, the problem is even greater. The design of shallow foundations in expansive clay is discussed in Chapter 9. A lump of clay on drying will be difficult to break with the fingers.